Tire alarm device

ABSTRACT

A tire alarm device gives a warning against the runflat operation limit of a pneumatic tire during runflat operation, the tire having a reinforcement layer disposed in each sidewall thereof for enabling the runflat operation. The device includes a tire temperature sensor used to warn of the runflat operation limit, and the tire temperature sensor is disposed on the inner surface of one of the sidewalls facing the reinforcement layer therein.

The present application claims priority based on Japanese PatentApplication No. 2003-110453, filed Apr. 15, 2003, the entirety of whichis being incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a tire alarm device that gives awarning against the runflat operation limit of a pneumatic tire duringrunflat operation, and more particularly, to a tire alarm device thatcan warn of the runflat operation limit with high accuracy.

TECHNICAL BACKGROUND

In response to demands in the market, there have been proposed manytechnologies which allow a vehicle to urgently travel (travel in arunflat mode) several hundred kilometers even when the pneumatic tire ispunctured while running; in recent years, safety tires and tire/wheelassemblies in which such technologies were put into practical use aregradually prevailing. Even when the inner pressure of the safety tiresor tire/wheel assemblies decreases due to, for example, puncturing, itis not easy to find the decrease in the tire inner pressure apparently;therefore, the safety tires and tire/wheel assemblies are required to beused in conjunction with an apparatus for monitoring the tire conditionbecause of assuring safety thereof.

As a conventional apparatus for monitoring the condition of a tire,Japanese Patent Application Publication No. 6-211012, for example,discloses a tire condition monitoring apparatus having an air pressuredetecting means for detecting the air pressure of a tire, a temperaturedetecting means for detecting the temperature of a tire, and a burstgeneration prediction means for predicting the generation of burst of atire based on the air pressure detected by the air pressure detectingmeans and the tire temperature detected by the temperature detectingmeans. Japanese Patent Application Publication No. 2000-355203 disclosesa tire air pressure warning apparatus that detects the air pressure of atire with a pressure sensor to inform the vehicle side of it by radio.

The above-described apparatuses can suitably be used as apparatuses formonitoring the condition of a normal pneumatic tire mounted on avehicle; however, when the above apparatuses are used for the foregoingsafety tires or tire/wheel assemblies, they can not give the driver awarning against the limit of runflat operation (the limit where theoperation is stopped before the breakdown of the tire) with highaccuracy during runflat operation.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a tire alarm devicewhich can warn the driver of the limit of runflat operation with highaccuracy during runflat operation.

In order to achieve the above object, the present invention provides atire alarm device that gives a warning against a runflat operation limitof a pneumatic tire during runflat operation having a reinforcementlayer disposed in each sidewall thereof for enabling the runflatoperation, comprising a tire temperature sensor to be disposed on aninner surface of one of the sidewalls facing the reinforcement layertherein, the tire temperature sensor being used to warn of the runflatoperation limit.

A pneumatic tire having a reinforcement layer disposed in each sidewallfor enabling runflat operation does not allow for runflat operation whenthe reinforcement layer that supports the load during runflat operationis heated and destroyed; as described above, because the tiretemperature sensor is placed on the inner surface of one of thesidewalls in the vicinity of the reinforcement layer therein, thetemperature of heat generated in one of the reinforcement layers thataffect the limit of runflat operation can be detected more precisely bythe tire temperature sensor; the runflat operation limit can be warnedof by using data of the temperature, thereby enabling the driver to begiven a warning against the runflat operation limit with high accuracyduring runflat operation.

The present invention provides another tire alarm device that gives awarning against a runflat operation limit of a pneumatic tire supportedduring runflat operation by a runflat support member mounted on a rim ofa wheel, comprising a tire temperature sensor to be disposed on asupport region of the runflat support member that supports the pneumatictire in contact therewith, the tire support sensor being used to warn ofthe runflat operation limit.

When the runflat support member is used, the tread of the pneumatic tirethat persistently engages the runflat support member during runflatoperation generates heat and is destroyed; as described above, bydisposing the tire temperature sensor in the support region of therunlfat support member near the tread, the temperature of the treadgenerating heat during runflat operation can be detected more preciselyby the tire temperature sensor, thereby enabling the driver to be givena warning against the runflat operation limit with high accuracy duringrunflat operation.

The present invention provides still another tire alarm device thatgives a warning against a runflat operation limit of a pneumatic tiresupported during runflat operation by a metallic support element of arunflat support member mounted on a rim of a wheel, comprising a tiretemperature sensor to be disposed on the metallic support element, thetire support sensor being used to warn of the runflat operation limit.

In the case where the runflat support member having a metallic supportelement is used as described above, by disposing the tire temperaturesensor on the metallic support element that is excellent in thermalconductivity, the temperature of the tread generating heat can bedetected more precisely by the tire temperature sensor, thus enablingthe driver to be given a warning against the runflat operation limitwith high accuracy during runflat operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a main cross-sectional view showing a state where the tireside unit of a tire alarm device according to the present invention isattached to the inner surface of a sidewall facing the reinforcementlayer therein.

FIG. 2 is an explanatory drawing showing an embodiment of a tire alarmdevice according to the present invention.

FIG. 3 is a graph showing an example of an approximate function f₀.

FIG. 4 is a main cross-sectional view showing an example of the tireside unit of a tire alarm device according to the present invention thatis attached to the runflat support member.

FIGS. 5 a and 5 b are main cross-sectional views showing other examplesof the tire side unit that is attached to the runflat support membershown in FIG. 4, respectively.

FIGS. 6 a and 6 b are main enlarged cross-sectional views showing stillother examples of the tire side unit that is attached to the runflatsupport member shown in FIG. 4, respectively.

FIG. 7 is a main cross-sectional view showing an example of the tireside unit that is attached to the metallic support element of a runflatsupport member.

FIG. 8 is an explanatory drawing showing another embodiment of a tirealarm device according to the present invention.

FIG. 9 is a graph showing an evaluation function f₁ for evaluating thedegree of risk according to the inner pressure of the tire.

FIG. 10 is a graph showing an evaluation function f₂ for evaluating thedegree of risk according to the running speed of the vehicle.

FIG. 11 is a graph showing an evaluation function f₃ for evaluating thedegree of risk according to the temperature of the tire.

FIG. 12 is a graph showing an example of a total evaluation function f₄.

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the attached drawings.

Referring to FIGS. 1 and 2, reference numeral 1 denotes a pneumatic tirethat can be operated in a runflat condition, reference numeral 2 denotesa tire side unit to be placed in a tire/wheel assembly X comprising awheel W having a rim R and the pneumatic tire 1 mounted on the rim R,and reference numeral 3 denotes a vehicle side unit to be mounted on avehicle.

The pneumatic tire 1 includes an innerliner 4 disposed on the inner sideof the tire, and carcass plies 6 provided outwardly of the innerliner,the carcass plies extending between left and right beads 5. The carcassplies 6 each has opposite end portions that are folded from the innerside of the tire toward the outer side thereof about bead cores 7embedded in the beads 5, with bead fillers 8 sandwiched therebetween.

Belt plies 10 are disposed radially outwardly of the carcass plies 6 ina tread 9, and a belt cover ply 11 is provided radially outwardly of thebelt plies. Disposed between the innerlier 4 and the carcass plies 6 ineach of sidewalls 12 is a cross-sectionally crescent-shapedreinforcement layer 13, formed of rubber, that allows for runfaltoperation; by supporting the load with the reinforcement layers 13during runflat operation, runflat operation is possible.

The tire side unit 2 comprises a tire temperature sensor 14 fordetecting the temperature of the tire, a tire inner pressure sensor 60for detecting pressure in the cavity of the pneumatic tire 1, and atransmitting means 15 for transmitting signals detected by the sensors14 and 60 to the vehicle side unit 3. The transmitting means 15 has atransmitter 15A and an antenna 15B, and the detected signals aretransmitted intermittently at prescribed intervals of time from theantenna 15B to the vehicle side unit 3.

The tire side unit 2 is attached to the inner surface region 12 a of oneof the sidewalls 12 facing the reinforcement layer 13 therein, so thatthe tire temperature sensor 14 is disposed in the vicinity of one of thereinforcement layers 13 that affect the limit of runflat operation.

The vehicle side unit 3 comprises a receiving means 17 having an antenna17A that receives the detected signals transmitted from the antenna 15Band a receiver 17B, a processing means 19 that determines whether or notthe tire has reached the zone of the run flat operation limit on thebasis of the detected temperature signal, and a warning means 20 thatinforms the driver of the runflat operation limit if the processingmeans 19 determines that the tire has reached the runflat operationlimit zone.

A memory 21 connected to the processing means 19 stores a preset limittemperature data corresponding to the runflat operation limit zone; theprocessing means 19 compares the value of temperature data of a signaldetected by the tire temperature sensor 14 with the value of the limittemperature data stored in the memory 21, and if the temperature datavalue of the detected signal exceeds the limit temperature data value,the processing means 19 determines that the tire has reached the runflatoperation limit zone, and outputs an operational signal to the warningmeans 20. The warning means 20 warns the driver of the runflat operationlimit with a sound, light or the like when receiving the input of theoperational signal. A clock means 22 that supplies time information datais connected to the processing means 19, and temperature data input tothe memory 21 from the processing means 19 are stored as time historydata of the temperature in the memory 21.

The processing means 19 also determines whether or not the value ofpressure detected by the tire inner pressure sensor 60 is below apredetermined threshold value stored in the memory 21 in advance, and ifthe detected pressure value is less than the predetermined thresholdvalue, the processing means determines that the tire is operated in arunflat condition. On the basis of this determination, the processingmeans determines whether or not the tire has reached the runflatoperation limit zone according to the temperature data described above.

The processing means 19 further calculates a sectional approximatefunction f₀ of the time history data of the temperature by using atleast four consecutive temperature data including the latest temperaturedata in the time history temperature data stored in the memory 21 if thedata values of temperature signals detected by the tire temperaturesensor 14 do not exceed the above limit temperature data value (see FIG.3). Specifically, the approximate function f₀ used preferably includes afunction having a quadratic or more polynomial such as f₀=at²+bt+c orf₀=at^(m)+c where a, b, c and m are coefficients and t is time (second);each of the coefficients may be obtained by using a least-squares methodor the like according to the function form. If the change of thetemperature tends to increase or to be constant, that is, if thecoefficient a is expressed by a≧0 when using the above-mentionedfunction form, the temperature values after the latest temperature dataare estimated in time series by an extrapolation method using theapproximate function f₀, because the tire has a high possibility ofreaching the runflat operation limit with the passage of time even ifthe tire has not reached the runflat operation limit at this time. Atime interval reaching the limit temperature data value is calculated,based on the estimated temperature values, and the calculated timeinterval is displayed by a displaying means 23 connected to theprocessing means 19; the processing means estimates the time intervaluntil the tire reaches the runflat operation limit zone to inform thedriver. If the change of the temperature tends to decrease, that is, ifthe coefficient a is expressed by a<0 when using the above-mentionedfunction form, the processing means does not estimate the time intervaluntil the tire reaches the runflat operation limit.

The value of the limit temperature data stored in the memory 21 isproperly selected in accordance with tire sizes and constructions, andmay generally be selected from the range of 50 to 150° C. The reason whyat least four consecutive temperature data including the latesttemperature data are employed is to capture the extreme changing of thetemperature more properly. Preferably, six consecutive temperature dataincluding the latest temperature data are used.

When the reinforcement layers 13 that support the load during runflatoperation are destroyed, the pneumatic tire 1 described above does notallow for runflat operation; in the process of reaching the destruction,the reinforcement layers 13 are repeatedly significantly deformed, sothe amount of heat generated therein is much greater, resulting in thatthe temperature thereof rises to a greater extent than that of otherparts. As the temperature is higher, the degree of risk of becoming therunflat operation limit is higher.

In the present invention, based on the knowledge, the tire side unit 2having a tire temperature sensor 14 is placed in the inner surfaceregion 12 a of one of the sidewalls 12 in the vicinity of thereinforcement layer 13 therein, so that the temperature of heatgenerated in the reinforcement layers 13 can be detected more preciselyby the tire temperature sensor 14 as the temperature of the tire, andthe runflat operation limit can be determined by the processing means 19using the temperature data, thereby being possible to give the driver awarning against the runflat operation limit with high accuracy duringrunflat operation.

If the data values of temperature signals detected by the tiretemperature sensor 14 do not exceed the limit temperature data value,the time interval reaching the runflat operation limit zone can beestimated, thereby informing the driver of the runflat operation limitin advance and allowing for the provision of information on the tireexchange time.

Referring to FIG. 4, the tire alarm device of the present inventiondescribed above is used for a tire/wheel assembly X′ comprising a wheelW having a rim R, a pneumatic tire 31, and a runflat support member 32mounted on the rim for supporting the pneumatic tire during runflatoperation. The pneumatic tire 31 has a normal construction without thereinforcement layers 13 described above.

The runflat support member 32 comprises an annular shell 33 formed of arigid material such as metal or resin, and left and right elastic rings34 formed of an elastic material such as elastic resin. When thetire/wheel assembly X′ is mounted on a vehicle and the pneumatic tire 31is punctured during traveling, the tread 31 a of the punctured pneumatictire 31 is supported by the radially outer support region 33X of theannular shell 33, which allows for runflat operation.

In a tire/wheel assembly X′ as described above, the tread 31 a thatpersistently engages the annular shell 33 during runflat operationgenerates heat and is destroyed, whereby runflat operation can not beperformed. Therefore, the tire side unit 2 is disposed in the supportregion 33X of the annular shell 33 that supports the tread 31 a inengagement therewith. In the example shown in the drawing, the supportregion 33X of the annular shell 33 comprises two convex support portions33A arranged in the widthwise direction of the shell and a concaveconnection portion 33B connecting the two convex support portions 33A,and the tire side unit 2 is attached to the inner surface of the concaveconnection portion 33B.

The tire side unit 2 maybe attached to the outer surface of the concaveconnection portion 33B as shown in FIG. 5 a, or may be placed on theinner surface of one of the convex support portions 33A as shown in FIG.5 b.

The tire side unit 2 may further be placed in a recess 35 formed in theouter surface of the annular shell 33 as shown in FIG. 6 a, or may bedisposed in a recess 35 formed in the inner surface of the annular shell33 as shown in FIG. 6 b. By putting the tire side unit 2 in the recess35 as described above, the tire side unit 2 can be attached to the outersurface of the convex end of the convex support portion 33A of thesupport region 33X, and placed in a position extremely close to thetread 31 a that generates heat during runflat operation.

When the annular shell 33 is composed of a metallic support element, thetire side unit 2 may be placed in any position of the annular shell 33such as in the surface of the annular shell 33 that is out of thesupport region 33X and is in the vicinity of one of the elastic rings 34as shown in FIG. 7 for example, if the tire side unit 2 is not broken,because the annular shell is very good in thermal conductivity.

As described above, the tire alarm device of the present invention canalso be preferably used for a tire/wheel assembly X′ in which therunflat support member 32 for supporting the pneumatic tire 31 duringrunflat operation is mounted on the rim R.

The runflat support member 32 is not limited to one having theabove-described structure, but may be a runflat support membercomprising, for example, a T-shaped or I-shaped insert ring or the likeattached to the rim R.

Referring to FIG. 8, there is shown another embodiment of the tire alarmdevice of the present invention, in which reference numeral 42 is a tireside unit to be disposed in the tire/wheel assembly X, X′ and referencenumeral 43 is a vehicle side unit to be mounted on a vehicle.

The tire side unit 42, which is attached to the same position asdescribed above, comprises a tire temperature sensor 44 for detectingthe tire temperature, a tire inner pressure sensor 45 for detectingpressure in the cavity of the pneumatic tire, and a transmitting means46 for transmitting signals detected by the tire temperature sensor 44and the tire inner pressure sensor 45 to the vehicle side unit 43. Thetransmitting means 46 has a transmitter 46A and an antenna 46B, and thedetected signals are transmitted intermittently at prescribed intervalsof time from the antenna 46B to the vehicle side unit 43.

The vehicle side unit 43 comprises a receiving means 48 having anantenna 48A that receives the detected signals transmitted from theantenna 46B and a receiver 48B, a speed obtaining means 50 for obtainingthe running speed of the vehicle from the vehicle, a processing means 51that determines whether or not the tire has reached the runflatoperation limit zone on the basis of the detected signals of the tiretemperature and tire inner pressure input from the receiving means 48,and the detected signals from the speed obtaining means 50, a warningmeans 52 that informs the driver of the runflat operation limit if theprocessing means 19 determines that the tire has reached the runflatoperation limit zone, a clock means for supplying time information datato the processing means 51, and a memory 54.

The memory 54, which is connected to the processing means 54, storesdata of the pressure, speed, and temperature output from the processingmeans 51 as time history data.

An evaluation function f₁ for evaluating the degree of risk according tothe tire inner pressure, an evaluation function f₂ for evaluating thedegree of risk according to the vehicle running speed, and an evaluationfunction f₃ for evaluating the degree of risk according to the tiretemperature are stored in the memory 54. These evaluation functions areobtained from experiments; examples of the evaluation functions areshown in FIGS. 9, 10 and 11.

FIG. 9 shows the evaluation function f₁ for evaluating the degree ofrisk according to the tire inner pressure, and this evaluation functionf₁ is expressed with a form that decreases monotonously as the innerpressure increases as follows:f ₁ =a ₁ ×e ^(−C1×P)where a₁ is a constant that is a positive real value, C1 is a constant,P is the ratio of the real air pressure of the tire (kPa) to the set airpressure of the tire (kPa), and e is the natural logarithm. The constanta₁ is preferably in the range of 10⁻¹ to 10¹, and the constant C1 in therange of 2.0 to 8.0. The constants a₁ and C1 are values that depend onthe size and construction of the tire and the like. The value detectedby the tire inner pressure sensor 45 is used for the real air pressureof the tire. In the graph of FIG. 9, the ratio P of the real airpressure of the tire to the set air pressure of the tire is plottedalong the abscissa, and the degree of risk along the ordinate.

FIG. 10 shows the evaluation function f₂ for evaluating the degree ofrisk according to the vehicle running speed, and this evaluationfunction f₂ is expressed with a form that increases monotonously as thevehicle running speed increases as follows:f ₂ =a ₂ ×V ^(C2)where a₂ is a constant that is a positive real value, C2 is a constant,and V is the ratio of the running speed of the vehicle (km/h) to thereference speed (100 km/h). The constant a₂ is preferably in the rangeof 10⁻¹ to 10¹, and the constant C2 in the range of 1.5 to 3.5. Theconstants a₂ and C2 are also values that depend on the size andconstruction of the tire and the like. The value obtained by the speedobtaining means 50 is used for the vehicle running speed. In the graphof FIG. 10, the ratio V is plotted along the abscissa, and the degree ofrisk along the ordinate.

FIG. 11 shows the evaluation function f₃ for evaluating the degree ofrisk according to the tire temperature, and this evaluation function f₃is expressed with a form that increases monotonously as the temperatureincreases as follows:f ₃ =a ₃ ×T ^(C3)where a₃ is a constant that is a positive real value, C3 is a constant,and T is the ratio of the tire temperature (° C.) to the referencetemperature (25° C.). The constant a₃ is preferably in the range of 4 to256, and the constant C3 in the range of 1 to 4. The constants a₃ and C3are also values that depend on the size and construction of the tire andthe like. The value detected by the tire temperature sensor 44 is usedfor the tire temperature. In the graph of FIG. 11, the ratio T isplotted along the abscissa, and the degree of risk along the ordinate.

The processing means 51 combines the above evaluation functions f₁, f₂and f₃ to form an expression shown by the following expression, which isa total evaluation function f4 for evaluating the degree of total risk.FIG. 12 shows a graph of an example of the total evaluation function.Time t is plotted along the abscissa, and the degree of total risk alongthe ordinate.f ₄ =m ₁ ×a ₁ ×e ^(−C1×Pt) +m2×a ₂ ×V _(t) ^(C2) +m ₃ ×a ₃ ×T _(t) ^(c3)

In the expression, m₁ to m₃ are weighting coefficients, and thecoefficients m₁ to m₃ are normally 1; however, when the degree ofcontribution to the inner pressure, speed, and temperature differs dueto the tire size and construction and the like, the coefficients m₁ tom₃ are properly modified accordingly. In this case, the coefficients m₁to m₃ may generally be selected from the range of 1 to 10. P_(t), V_(t)and T_(t) are values obtained by the tire inner pressure sensor 45,speed obtaining means 50 and tire temperature sensor 44 according totime, respectively.

Next, the processing means calculates the temporal integration valueF_(t-t1) of an interval between the time t₁ of the data just one beforethe data having the latest time t₂ and the time t₁-t₀ that goes back atime period t_(o) from the time t₁, using the total evaluation functionf₄, as shown in the expression below. The time period t₀ is preferablyin the range of time such that, in data obtained intermittently from thetire side unit 42, the number of data in the integral interval is about5 to 100. When the data are obtained at five second intervals, forexample, the time period may be in the range of about 25 to 500 seconds.If the time period t₀ is too short or long, a proper estimate can not bedone. In particular, if the time period is too long, there is a riskthat a proper estimate can not be done when the temperature changesquickly.F _(t=t1)=∫_(t) ₁ _(−t) ₀ ^(f) ¹ ƒ₄ dt

The processing means further calculates a reference value f_(c) used fordetermination of the runflat operation limit from the integration valueF_(t=t1), using the following expression.F _(c) =F _(t=t1) /t ₀

Then, if the following expression is fulfilled, using the value f_(t2)of the total evaluation function f₄ at the latest time t₂, referencevalue f_(c) and limit value L stored in the memory 54 in advance, theprocessing means determines that the tire has reached the runflat limitzone, and the warning means 52 gives the driver a warning against therunflat operation limit.f _(t2) /f _(c) >L

When a tire has reinforcement layers 13, the limit value L depends onthe thickness, properties, etc. of the reinforcement layers 13, and whena tire has no reinforcement layers 13 and the runflat support member 32is used, the limit value L depends on the material, thickness, shape,etc. of the annular shell 33 of the runflat support member 32 as well asthe material, thickness, shape, etc. of the elastic rings 34; the limitvalue is properly set in the range of 2 to 5.

The values of the total evaluation function f₄ that have been calculatedsequentially are serially input from the processing means 51 to thememory 54, and stored as time history data.

The processing means 51 also determines whether or not the values of thepressure detected by the tire inner pressure sensor 45 are below aprescribed threshold value prestored in the memory 54, and if thedetected pressure values are less than the prescribed threshold value,the processing means determines that the tire is operated in a runflatcondition. If the processing means determines that the tire is operatedin the runflat condition, the processing means determines whether or notthe tire has reached the above runflat limit zone.

The processing means 51 further calculates a sectional approximatefunction f′₄ of the total evaluation function f₄ by using at least fourconsecutive data including the latest data in the time history data ofthe values of the total evaluation function f₄ stored in the memory 21if the processing means 51 determines that the latest data does notexceed the limit value of the degree of risk; the processing means thenestimates the values of the total evaluation function f₄ after thelatest data in time series by an extrapolation method using thesectional approximate function f′₄. The approximate function f′₄ usedpreferably includes a function having a quadratic or more polynomialsuch as f′₄=Ax²+Bx+C or f′₄=Ax^(n)+C where A, B, C and n arecoefficients and x is time (second); each of the coefficients may beobtained by using a least-squares method or the like according to thefunction form.

The processing means 51 calculates a time interval until the tirereaches the runflat operation limit zone, using the values estimated intime series and the limit value L, and the calculated time interval isdisplayed by the display means 55 connected to the processing means 51;the time interval until the tire reaches the runflat operation limitzone can be projected.

The present inventor has found the following through an intense studyand various experiments about the limit as to the runflat operation.

As the tire inner pressure is lower, the degree of risk of becoming therunflat operation limit is higher; as the running speed of a vehicle isfaster, the degree of risk of becoming the runflat operation limit isgreater; as the tire temperature is higher, the degree of risk ofbecoming the runflat operation limit is further increased; it has beenfound that evaluation functions f₁, f₂ and f₃ that evaluate the degreeof risk described above are expressed by expressions that change in anonlinear manner as explained above.

These evaluation functions f₁, f₂ and f₃ are correlative to each other,and can be connected as the total evaluation function f₄ havingvariables according to time as described above; by determining therunflat operation limit as described above on the basis of the temporalintegration value F_(t=t1) and the preset limit value, the runflatoperation limit can be determined with high accuracy during runflatoperation.

The above-described total evaluation function f₄ is defined by the sumof the functions f₁, f₂ and f₃ multiplied by the weighting coefficients,respectively, but the total evaluation function f₄ may be expressed asfollows.f ₄ =a ₁ ×e ^(−C1×Pt×m1) +a ₂ ×V _(t) ^(C2×m2) +a ₃ ×T _(t) ^(C3×m3)The limit value L used here is modified to be a value according to theexpression.

As described above, according to the another embodiment of the presentinvention, the processing means determines whether or not the tire hasreached the runflat operation limit zone on the basis of the temporalintegration value of the total evaluation function f₄ and the presetlimit value L, thereby enabling the driver to be given a warning againstthe runflat operation limit with higher accuracy during runflatoperation.

Since the time interval until the tire reaches the runflat operationlimit zone can be estimated, the driver can be informed of the runflatoperation limit in advance and provided with information on the tireexchange time.

In the present invention, the tire side unit 42 may separately bestructured so as to have a unit including the tire temperature sensor 44and a unit including the tire inner pressure sensor 45; the unitincluding the tire temperature sensor 44 is attached in the vicinity ofthe high-heat generation region as described above while the unitincluding the tire inner pressure sensor 45 is placed on the rim R orthe like.

The processing means 51 is preferably structured so that the processingmeans makes the memory 54 store data of the tire inner pressure, runningspeed and tire temperature as respective mapped data at the initialstage of the tire when the tire is run up to about 1000 km after thetire inner pressure is set to a vehicle's recommended air pressure (airpressure indicated in a vehicle, or air pressure stated in JATMA (year2002) if not indicated in the vehicle) at the point of purchase of a newvehicle or at the point of tire exchange, and calculates means values ofthe respective mapped data as respective reference data of the tireinner pressure, running speed and tire temperature, and compares thereference data with data of the tire inner pressure, running speed andtire temperature obtained during traveling after the tire initial stageto calculate the amount of deviations from the reference data. Thisallows the condition of the tire to be easily verified during normaloperation after the tire initial stage.

While preferred embodiments of the tire alarm device has hereinabovebeen described, it will be understood that the present invention is notlimited to the above embodiments but covers all modifications as may beincluded within the scope of the invention as defined by the appendedclaims.

INDUSTRIAL APPLICABILITY

The tire alarm device of the present invention having the aforementionedexcellent effects can be very effectively utilized as a tire alarmingdevice that gives a warning against the runflat operation limit of apneumatic tire during runfalt operation.

1. A tire alarm device that gives a warning against a runflat operationlimit of a pneumatic tire during runflat operation having areinforcement layer disposed in each sidewall thereof for enabling therun flat operation, comprising: a tire temperature sensor disposed on aninner surface of one of the sidewalls facing the reinforcement layertherein, the tire temperature sensor being used to warn of the runtlatoperation limit, a processing means that determines whether or not thetire has reached a zone of the runflat operation limit based on a signaldetected by the temperature sensor; a warning means that gives a warningif the processing means determines that the tire has reached the runflatoperation limit zone; a tire side unit having the tire temperaturesensor; and a transmitting means that transmits the signal detected bythe tire temperature sensor, and a vehicle side unit having a receivingmeans that receives the signal from the transmitting means, theprocessing means and the warning means, wherein the vehicle side unithas a memory that stores a preset limit temperature data according tothe runflat operation limit zone, and wherein the processing meanscompares a temperature data value of the signal detected by the tiretemperature sensor with a value of the limit temperature data, anddetermines that the tire has reached the runflat operation limit zone ifthe temperature data value of the detected signal exceeds the limittemperature data value, wherein the tire side unit has a tire innerpressure sensor for detecting pressure in a cavity of the pneumatictire, and wherein the processing means determines whether or not a valueof the pressure detected by the tire inner pressure sensor is below aprescribed threshold value, and determines that the tire is operated ina runflat condition if the detected pressure value is less than theprescribed threshold value, and determines whether or not the tire hasreached the runflat operation limit zone if the processing meansdetermines that the tire is operated in the runflat condition, andwherein the memory stores time history data of the temperature detected,and wherein the processing means calculates a sectional approximatefunction of the temperature time history data by using at least fourconsecutive temperature data including a latest temperature data in thetemperature time history data stored in the memory if the processingmeans determines that the tire has not reached the runflat operationlimit zone, and estimates values of the temperature after the latesttemperature data in time series by an extrapolation method using thesectional approximate function, and calculates a time interval reachingthe limit temperature data value on the basis of the estimatedtemperature values.
 2. A tire alarm device that gives a warning againsta runflat operation limit of a pneumatic tire during runflat operationhaving a reinforcement layer disposed in each sidewall thereof forenabling the runflat operation, comprising: a tire temperature sensordisposed on an inner surface of one of the sidewalls facing thereinforcement layer therein, the tire temperature sensor being used towarn of the runflat operation limit; a tire inner pressure sensor fordetecting pressure in a cavity of the pneumatic tire; a speed obtainingmeans for obtaining a running speed of a vehicle on which the pneumatictire is mounted; a processing means that determines whether or not thetire has reached a zone of the runflat operation limit based on signalsfrom the tire temperature sensor, the tire inner pressure sensor and thespeed obtaining means; and a warning means that gives a warning if theprocessing means determines that the tire has reached the runflatoperation limit zone, wherein the processing means calculates a temporalintegration value obtained by integrating by time a total evaluationfunction f₄ that is a combination of an evaluation function f₁ forevaluating degree of risk according to the tire inner pressure, anevaluation function f₂ for evaluating degree of risk according to thevehicle running speed and an evaluation function f₃ for evaluatingdegree of risk according to the tire temperature and has variablesaccording to time, and determines whether or not the tire has reachedthe runflat operation limit zone based on the temporal integration valueand a preset limit value L.
 3. A tire alarm device according to claim 2,comprising a memory storing the preset limit value L, the processingmeans comparing the temporal integration value with the preset limitvalue L and determining that the tire has reached the run flat operationlimit zone if the temporal integration value exceeds the preset limitvalue L.
 4. A tire alarm device according to claim 3, wherein theprocessing means determines whether or not a value of the pressuredetected by the tire inner pressure sensor is below a prescribedthreshold value, and determines that the tire is operated in a runflatcondition if the detected pressure value is less than the prescribedthreshold value, and determines whether or not the tire has reached therunflat operation limit zone if the processing means determines that thetire is operated in the runflat condition.
 5. A tire alarm deviceaccording to claim 4, wherein the memory stores values of the totalevaluation function f₄ as time history data, and wherein, if theprocessing means determines that the tire has not reached the runflatoperation limit zone, the processing means calculates a sectionalapproximate function f'₄ of the total evaluation function f₄ by using atleast four consecutive data including a latest data in the time historydata of the values of the total evaluation function f₄ stored in thememory, and estimates values of the total evaluation function f₄ afterthe latest data in time series by an extrapolation method using thesectional approximate function f'₄, and calculates a time interval untilthe tire reaches the run hat operation limit zone, using the valuesestimated in time series and the limit value L.
 6. A tire alarm deviceaccording to claim 2, comprising a tire side unit having the tiretemperature sensor, the tire inner pressure sensor and a transmittingmeans that transmits the signals detected by the tire temperature sensorand the tire inner pressure sensor, and a vehicle side unit having areceiving means that receives the signals from the transmitting means,the processing means and the warning means.